Tin Whiskers Again Cited as Potential Problem for Toyotas

The debate over the role of tin whiskers in Toyota's unintended acceleration case has returned, and government administrators are expected to answer more questions on the subject this week.

Even after the National Highway Traffic Safety Administration (NHTSA) declared in 2011 that there was no electronic cause for Toyota's problems, the debate had quietly continued. It rose to prominence again this month, when a US senator stepped in.

"Recently, whistleblowers have provided my office with information, supported by documentation, which raises concerns that the scope of the NHTSA and NASA investigations may have been too narrow," Sen. Charles E. Grassley (R-IA) wrote in a letter (PDF) to NHTSA Administrator David Strickland on July 12. The letter went on to pose questions about the agency's methodology, and it called for answers to be delivered by July 26.

Toyota's Matrix is one of the vehicles recalled during the automaker's "unintended acceleration" studies.(Source: Toyota)

Tin whiskers -- small metal dendrites that sometimes form on electroplated tin -- are an important topic for design engineers, because they can cause short circuits and arcing in electrical equipment. In Toyota's case, tin whiskers were considered a potential culprit in the "unintended acceleration" claims that grabbed headlines three years ago.

Much of the debate over tin whiskers died down in February 2011, after Secretary of Transportation Ray LaHood called on teams of NHTSA and NASA engineers to search for the cause of Toyota's problems. "The verdict is in," LaHood declared emphatically after the scientists reached their conclusion. "There is no electronic-based cause for unintended high-speed acceleration in Toyotas. Period."

After that conclusion was announced, the National Academy of Sciences said that all available data indicated there was no electronic or software problem on the Toyotas.

Still, the buzz about tin whiskers continued in some quarters, especially after a separate team of NASA scientists published a study (PDF) of Toyota accelerator pedals on the Internet in September 2011. The scientists said they found tin whiskers in an accelerator assembly, and "a tin whisker induced short was responsible for the failure of a 2003 Toyota Camry Accelerator Pedal Position (APP) Sensor based on a Dual Potentiometer Design."

In his letter, Grassley cited that study and its author, Henning Leidecker of NASA Goddard, to support his claim that more questions needed to be answered.

In response to the latest volley, Toyota officials argued that tin whiskers may cause failure of pedal sensors, but they've never caused unintended acceleration. "We know that tin whiskers can form -- we've never said they couldn't," Brian Lyons, a spokesman for Toyota, told us. "But when pedals fail -- for whatever reason -- the vehicle enters into a fail-safe situation, a limp-home mode."

Lyons also said that the September 2011 study specifically linked tin whiskers to sensor failure in the accelerator assemblies, not to unintended acceleration.

When reports of unintended acceleration originally surfaced, Toyota engineers examined multiple potential culprits: the accelerator's friction lever, heater condensation, corrosion, electronics, and floor mats. Toyota has since examined the mats, shortened the pedals, lengthened the friction lever, added a spacer, and changed the linkage materials. It also employs a brake-throttle override on its vehicles to cut off gas flow if the brake and accelerator pedals are depressed simultaneously.

Until Grassley sent his letter to the NHTSA, the focus had shifted away from electronics and toward floor mat entanglements. In June, the NHTSA mandated a recall of 154,000 more Toyota vehicles for problems associated with "unsecured or incompatible floor mats."

Hopefully rather than to point fingers or cast blame, this on-going debate will serve to spotlight the issue of tin whiskers and keep the potential problem on the front burner as engineers hit the drawing board on future designs. Obviously, it's a critical issue and potentially, a deadly problem if overlooked. So maybe the continued attention is a good thing.

Keeping the tin whisker problem on the forefront should help with future designs. Toyota is also very concerned with the floor mat issue. Our Toyota is a 2011, and the required 5000 mile preventive maintenance requires a floor mat inspection each time. They want to be sure this issue does not materialize again.

With two teenagers, my wife and I have 4 drivers in our household. We've owned 4 Toyota Corollas and are currently driving 3 of them which vary from 15k to 150k miles. We keep returning to Toyota because of the reliability and systematic build quality. I don't wish to bash the manufacturer, but we recently salvaged my wife's German car that was losing components faster than we could earn money to replace them. After we lost the transmission at 75K miles this summer, we traded it in for a two-year-old Corolla. Performing home repairs was near impossible and even a check of the transmission fluid level required a car lift and the removal of guards and plates under the car in order to reach the fill plug. The instructions for checking the level was to remove the plug and observe how much fluid escaped.

The Toyotas are extremely maintenance-friendly and our independent mechanic is delighted when we bring them in for routine service and inspection. Each component is designed with the other components in mind and the car as a whole is a tightly-integrated system even though (because) the individual components are not engineered to fine Swiss-craftsmen tolerances. I'm delighted to hear the Toyota engineers are being open with the debate.

Hi ttemple... As a System Designer I praise good design whenever I see it. Electronics, hardware, software, education, administration - Like "fine art", I can recognize good design when I see it and like to praise it highly.

It is a personal quirk of mine not to bash poor design. The trouble and expense we have had over the past five years of owning the "German" car were not individual lemon problems with bad components --- it was an overall failure of system design. The layout of the parts was a perfect example of "fallacy of sub-optimization". It is wrong-headed to think that if all sub-components are optimized to near-zero tolerance the overall system will be improved. The truth is exactly the opposite.

System Design should concentrate on how out-of-tolerance behavior will be accommodated by the system as a whole, making it fault-tolerant and adaptive. The Toyota "J-Factor" is incorporated throughout the corporate culture (see here for example) and has been described recently:

"J-factor is known to be the DNA of Toyota design that synergizes various conflicting elements in harmony and give dimensions to new values. It is the element that defines the Japanese design structure, aesthetics and values that blend seamlessly with the global standards. One very good example of synergizing the contradictory element is the combination of engine power and electric motor to create hybrid vehicles. Likewise, many other elements of a car are well harmonized to give a completely new look and feel to every car. The j-factor is the trademark of Toyota's car design and it delivers an extremely striking and magnificent appeal." - link here

After our story was turned in, NHTSA came back to us with a written statement about its position on this matter. There's not an iota of change in NHTSA's position, but I think it's worth posting anyway:

"As NHTSA and NASA indicated in our reports, the occurrence of "tin whiskers" is exceedingly rare and even when they are present, they do not appear to present any significant danger to drivers. We found that even if these tin whiskers created a small electrical short, they would not affect a driver's braking ability and would not cause the vehicle to accelerate out of control. As we identified and discussed in the reports, we have no reason to believe this could present a danger to drivers.

"In fact, NHTSA only knows of four occurrences of tin whiskers in a population of 1.7 million Camry vehicles. None of those occurrences involved any crashes or injuries and in each case, the vehicle entered a form of fail-safe operation that was so noticeable that the consumer quickly brought the vehicle in for repair."

One of them is Bob Landman of HL Instruments. He and several others in NASA GSFC have been studying this problem for years.

This issue of tin whiskers is not new, and it is insidious. It was discovered during WW II and it is the reason we use lead based solder. Unless a solder is made with at least 3% lead alloy, it will start forming whiskers. The exact mechanism that causes this is not known, but the experimental evidence is incontrovertible.

All this nonsense got started because of the highly political and ignorant RoHS effort by the EU. Lead, as a material, has for all intents and purposes been declared "evil". I understand that we want to eliminate toxic waste from electronics, but if we make devices that become unreliable after just three years of servicesince manufacture (the average time it takes to grow a whisker to an adjacent contact), how environmentally sound is that?

Furthermore, with all the RoHS stuff in the supply chain, it is getting increasingly difficult to buy parts that aren't RoHS. Many will re-label parts as lead based, when they're not. This is very disconcerting to those who build high reliability devices or long lived devices such as spacecraft or safety systems.

Some progress has been made on a treatment that can be used to mitigate this problem, but it is still a long, intractable, and difficult issue.

Toyota is hardly the only company wrestling with this problem. This is an industry-wide problem that requires a political solution. The RoHS standards have run amok and need to be reigned in.

Jake Brodsky

PS: I wrote "3 years of service" when I should have written "3 years since manufacture." Whiskers will grow whether the equipment is in service or sitting on the shelf.

Tim, even more interesting was the experience of buying a new toyota recently, at delivery the sales person came out and gave me a canned pecture on the floor mats.

My experience after 2 months of driving it are that the pedals are not laid out particualry well for a tall person with big feet. On a couple of occasions I have hit the accelerater by accident and had trouble getting my foot off.

I do get depressed when senators decide to do design work however. They can't pass a budget but they can design electronic automobile controls

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